This article highlights one of the biggest issues with Apple Music: that it forces you to use iTunes Match, something that has been around for a year (and is absolutely awful, and has not improved). It is a mess.
http://www.theverge.com/2015/7/1/8877129/apple-music-icloud-problems
Beyond that, iTunes on Windows doesn't scale to high DPI displays and looks either incredibly ugly, or the UI elements are broken, depending on the type of scaling you use (MS has created thorough APIs for scaling and has had them for years, since before Windows 7. Apple has never updated iTunes to follow them, and in fact the new iTunes design scales even worse than the old one).
Music the service itself has some issues, but it is not bad. The biggest issues are Match ruining people's existing music collections and infecting Music with wrong copies of songs, with no way of fixing it, as well as the bad iTunes interface. Even if they fix the Music service issues (Beats1 going offline, people getting errors playing certain songs) the whole package will still be broken because iTunes will still be broken.